1. Field of the Invention
This invention relates to pipe laying apparatus and, more particularly, to an apparatus for pulling an adjacent section of pipe into abutting contact with a previously laid pipe section.
2. Description of the Prior Art
Recently OSHA has mandated that contractors who install relatively large pipes in open trenches must use a trench box during the installation process. The trench box consists of a pair of large rectangular steel plates positioned vertically on either side of the trench where a section of pipe is being installed. The vertical dimension of each steel plate must be sufficient to protrude several feet above the upper surface of the trench, while the horizontal dimension of each steel plate must be slightly longer than the length of each pipe section. The vertical positioning and the spacing between each of the rectangular steel plates is maintained by horizontally oriented struts which extend between the upper end portions of the steel plates.
As the pipe-laying operation progresses, the trench box is lifted by a crane to the next area of the trench in which a newly positioned pipe section must be longitudinally aligned and fitted with the previously laid pipe section.
While the trench box increases the safety of workers who are responsible for fitting the abutting sections of pipe together within the trench, it has made the use of a number of prior art pipe laying machines somewhat more difficult.
One prior art pipe laying device is disclosed in the Forsberg patent (U.S. Pat. No. 3,561,615). The Forsberg device requires a telescopically extendable frame, tension springs, and grapples. It must be fitted to adjacent sections of pipe at four points. Since it is longer than a single pipe section, it is frequently difficult to use within a trench box.
A second prior art device for positioning and assembling sections of pipe is disclosed by Vigeneron (U.S. Pat. No. 3,036,372). This mechanism similarly is extremely elaborate and sophisticated. Since it too must be lowered into position from above by a crane and must have a length slightly greater than the length of a single pipe section, a trench box tends to restrict its usefulness.
A third prior art pipe laying apparatus is disclosed in a patent issued to Wiswell (U.S. Pat. No. 3,657,786). The Wiswell apparatus consists of a tripod-like structure, two legs of which are supported by the earth on either side of the trench, while the third leg is supported by the previously laid pipe section. This device is intended for use in underwater pipe laying operations where only very shallow trenches are required. It is not compatible with deep trench pipe laying operations.
As can be seen by a study of the three above mentioned patents, not only is each of these devices difficult to use with a trench box, but each is also bulky, heavy, mechanically complex, and can only be repositioned by a crane or some other similar lifting mechanism. Transporting these devices to the location where pipe sections are to be laid requires either a very large truck or a specially designed trailer. These devices are of such great length that they cannot readily be transported in smaller trucks without substantial disassembly.
Because of the high cost and complexity of prior art pipe laying systems, pipe laying contractors frequently use manual mechanical systems. These mechanical systems typically consist of a chain used in combination with a rachet wrench. A chain is wrapped around the circumference of one pipe and the circumference of a previously laid pipe section. The rachet is manually operated until the two pipe sections are drawn into proper abutting contact.
The use of the chain and rachet combination is very time consuming and requires a number of positioning and fastening steps before it can be activated. Because of the degree of mechanical advantage required, the amount of chain moved over the rachet during each take-up operation is very minimal so that a relatively large number of rachet rotations is required to bring the two abutting sections of pipe into proper alignment.